Acoustic noise interferometry in a time-dependent coastal ocean

Area of Science:

• Oceanography
• Acoustics
• Geophysics

Background:

• Passive acoustic interferometry uses ambient noise to probe ocean properties.
• Coastal ocean environments exhibit temporal variability affecting noise analysis.
• Green's functions retrieval from noise requires significant averaging times.

Purpose of the Study:

• To develop a theory quantifying environmental nonstationarity effects on noise cross-correlations.
• To understand frequency limitations in acoustic noise interferometry due to ocean variability.
• To explore the potential of coherence loss in passive acoustic remote sensing.

Main Methods:

• Theoretical development of nonstationarity effects on two-point correlation functions.
• Analysis of diffuse noise cross-correlations.
• Comparison of theoretical predictions with experimental data from the Florida Straits.

Main Results:

• Ocean temporal variability imposes an upper limit on the usable frequency range for Green's function approximation.
• Theoretical predictions align quantitatively with experimental results.
• Coherence loss at high frequencies restricts passive acoustic remote sensing to lower frequencies, impacting inversion resolution.

Conclusions:

• Environmental nonstationarity is a key factor limiting passive acoustic remote sensing resolution.
• The observed coherence loss contains valuable information on unresolved ocean dynamics.
• Passive acoustic remote sensing can be enhanced by understanding and utilizing coherence loss.